All the laws are summed up in the one expression: Do not that to another, which thou wouldest not have done to thyself.
The laws of nature he regards as always binding _in foro interno_, to the extent of its being desired they should take place; but _in foro externo_, only when there is security.

As binding _in foro interno_, they can be broken even by an act according with them, if the purpose of it was against them.

They are immutable and eternal; 'injustice, ingratitude, &c., can never be made lawful,' for war cannot preserve life, nor peace destroy it.

Their fulfilment is easy, as requiring only an unfeigned and constant endeavour.
Of these laws the science is true moral philosophy, _i.e._, the science of good and evil in the society of mankind.

Good and evil vary much from man to man, and even in the same man; but while private appetite is the measure of good and evil in the condition of nature, all allow that peace is good, and that justice, gratitude, _&c._, as the way or means to peace, are also good, that is to say, _moral virtues_.